Certain acetals, such as acetaldehyde acetals, are used as organic solvents and plasticizers. These acetals are also utilized in the synthesis of a variety of other organic compounds. Acetaldehyde acetals can be prepared via acid catalyzed reactions of acetaldehyde and alcohols. For example, acetaldehyde diisopropyl acetal can be synthesized from acetaldehyde and isopropanol in 40-60% yields. Not only is the yield of this acetal in need of improvement, but large quantities of aqueous waste materials such as aqueous calcium chloride are generated from this reaction which creates a disposal problem.
Acetaldehyde diisopropyl acetal can also be synthesized by reacting vinyl acetate and isopropanol in the presence of a mercuric oxide/boron trifluoride catalyst. This reaction produces an even lower yield of the acetaldehyde diisopropyl acetal, about 38%. The reaction proceeds efficiently when primary alcohols are used, but yields suffer when secondary alcohols are employed. Further, mercury-based catalysts are increasingly disfavored because mercury is highly toxic and can be difficult to remove from organic products.
Japan Public Patent Disclosure Bulletin No. 57-35535 discloses a method for manufacturing acetals wherein vinyl esters and alcohols are reacted in the presence of a palladium chloride catalyst which is supported on an active carbon support. The disclosure states that the reaction can be accomplished only by using an active carbon support.
Industry is searching for efficient processes for producing acetals and hemiacetal esters wherein secondary and tertiary alcohols can be used as reactants. Moreover, improved catalysts are desired which are not based on mercury and which do not require active supports to provide sufficient conversion and selectivity.